Well drilling fluid



?atented Nov 23, 13

WELL DRILLING FL Tirey Foster Ford and Albert G.

Calif Delaware Loomis, Berkeley,

assignors to Shell Development Company, San Francisco, CaliiL,

a corporation of No Drawing. Application June 20, 1939, Serial No. 280,065

3 Claims.

taining a sufiicient hydrostatic head on the well to prevent an escape of gas from high pressure formations encountered.

A satisfactory drilling fluid must be essentially colloidal in character in orderto prevent settling of the cuttings in the borehole, must possess a suitably low viscosity to be circulated without excessive strain by the pumping equipment, a relatively low yield point to allow a ready release of the cuttings and entrained gases in settling pits,- and a sufliciently high specific gravity to maintain the desired hydrostatic head on the well and hold down the gas pressures. Weighting materials such as barytes, litharge, iron oxide, etc., are commonly added to drilling fluids to increase their specific gravity.

In order to prepare drilling fluids possessing as far as possible all these desirable properties, it has been customary to treat clay suspensions with various chemical agents, such as alkali hydroxides, carbonates, phosphates, silica es, tannates, humates, etc., or any combination thereof.

It has also been known that drilling fluids may be treated with pyrogenic derivatives of orthophosphoric acid, for example, with sodium hexametaphosphate, commercially known as Calgon," or with sodium or potassium pyrophosphates.

The effect of alkali metaphosphates, and especially of alkali pyrophosphates on the viscosity of drilling fluids appears to be superior to that of all other peptizing or deflocculating agents, reducing in some cases the viscosity of drilling fluids by as much as 82 or 83 percent of the original value. Theoretical considerations strongly indicate that these figures represent substantially the maximum reduction effect which may be achieved by chemical means, and that the possibility of eifecting sensibly greater viscosity reductions than those indicated is highly improbable.

The use of alkali meta and pyrophosphates as I viscosity reducers for drilling fluids is, however,

open totwo main objections.

First, the efiect of alkali meta and pyrophosphates on the viscosity of drilling fluids is relatively critical, that is, an addition of these agents to drilling fluids in'quantities greater than that necessary for a maximum reduction of viscosity results in a reversion to higher viscosities. This necessitates a close and accurate chemical control.of the process, and tends to increase its cost.

Second, the effect of alkali meta and pyrophosphates on drilling fluids is not permanent, that is,

drilling fluids whose viscosity had been reduced by means of these agents to a low value tend to revert to a high viscosity on standing or while in use in drilling wells, where this effect is even aggravated by the whipping and churning action of the drill string. d

It is, therefore, the-object of this invention to provide a treating agent for drilling fluids which, while substantially as effective as alkali meta and pyrophosphates in reducing the viscosity of drilling fluids, is not critical with regard to the quantities used, and is capable of producing a viscosity reduction eiiect of considerably greater permanence than said agents.

It has been found that such atreating agent can be obtained by subjecting pyrogenic derivatives of ortho-phosphoric acid to a further pyrogenic treatment, for example, by fusing together at high temperatures alkali metaphosphates with alkali pyrophosphates, whereby compounds known as polyphosphates are obtained.

The identity of various alkali polyphosphates has been considered by Mellor (Treatise on Inorganic and Theoretical Chemistry), who found that they conform to the general formula decaphosphates, trldecaphosphates,nondecaphosphates, etc., may equally well be used:

Table! Compound Formula mg 'lri hosphate NarPrOu lNarPnOM-GNmPaOr. Teigaphosphato NmPrOu lNsePion -iflalleoz. Heptaphosphate Na|P n manhole-momma Nonaphosphate NInP'Oa.-- minnow-summon Tetmdecaphosphato 'NlioPnou- 2NaPQOir TINMPIOL Eicosaphosphato NanPa0n- 3Naelcoir-lNaqPr0-z- In applying the treatment of the present invention to oil wells, the above agents, preferably in the form of an aqueous solution, may be added to the drilling fluid at a point near the intake of the circulating .pumps, which insures a thorough mix 1 ing of the solution with the-mud during circulation. The drilling fluid itself may be'iormed from clays present in the bore, or may be compounded outside the borehole irom any clay, such, !or example, as bentonite. Weighting materials such as hematite, barytes, galena, etc., may be incorporated in the mud if desired.

The amount or the treating agents is adjusted according to the properties of the drilling fluid, and also to a certain extent according to the character of the strata drilled through, but in Table II v [110 gms. oi Lebeo mud (specific gravity 1.19)]

Per cent Stormer viscosity reduc- Quantity of treating agent in c. c. of a 10% solution Sodium polyphosphaies Tetra 0mm cusses senses From Table Ii it will be seen that the polyphosphates are as effective as pyrophosphates in reducing the viscosity of drilling fluids, and that they possess, moreover, the additional advantage of causing substantially no reversion to higher viscosities ii excess is used. This property is or especial importance, first, because it eliminates the necessity and the costof close chemical control, and second, because it permits greater quantion for the various treating agents titles of the reagent to be added to the mud without impairing its quality when itis first compounded, thus eliminating the necessity oi retreating the mud at frequent intervals as the drilling proceeds.

\ TobleHl [Original oinrummgnasdeterminedbytbofltmmer viscometoratwo .P.M.4c.o.oial0%treatingsolutionm lddodtoeodioithewgr. samples, which weretbenplneodin 8oz .bottlelandvigorouslyshakenbyamechanimlshaku.]

Stunner viscosity in grams and per cent lowering elected by treatment Treating went treatment 6 hours 27 hour! 120 581%) 290 54 o) 82%) 160 a) 41) 34%) 118 81%) 210 67%) 2m fig 120 81%) 2&0 (64%) 320 Table IV [Original viseositiol'themud: 825 gr. as determined by the Stormer visoometeratm P. M.2c.c.oial0%trastingsolutlonwere addedtoeachllo .ottbeaeveralssm mgnofeachum is were then placed 600 c. 0. bottles and subjected to flmt lfi rolling (at about 100 n. r. M.) for 16 hours, and resting for 8 hours.

- Btormer viscosity in grams and per cent lowering enacted by treatment Treating agent Alter Alter Alter treatment so hours 284 hours Sodium pyrophosphate 100 (21%) 262 50%) no use 3) Sodium triphosphato 1m (81%) 1B5 15%) 245 (63%) Sodium tetraphosphate 100 {817 170 68%) 33) 37%) Sodium decaphosphate 100 81% 72%) 230 56%) is practically without effect on the drilling fluid viscosity. By contrast, in an identical drilling fluid reduced with a polyphosphate and thickened to the same viscosity by shaking, relatively small additional quantities of the polyphosphates are sufllcient for retreating the drilling fluid and, again reducing its viscosity to a desired low value.

It must further be pointed out that although alkali polyphosphates are highly efiective in reducing the viscosities of any clay suspensions, weighted or not. such as are used in compounding drilling fluids, their eflect is even more marked in suspensions of materials having a similar or related composition, for example, in suspensions of colloidal phosphate rock, or in colloidal clay suspensions weighted with brushed phosphate rock.

Crushed and ground phosphate rock, when suspended in suitable concentrations in an aqueous medium, forms drilling fluids which compare favorably in specific gravity with weighted clay suspensions. Since phosphate rock is a readily available and cheapmaterial, its use for drilling fluids obviates the necessity or using such relatively costly materials as barytes; red'lead, etc. However, the viscosity of such heavy phosphate rock suspensions is considerably higher than per- Alkali polyphosphates, however, due to a phenomenon or adsorption on the surfaces of the ground phosphate rock particles, are eilective in and small percentage of a water-soluble polyreducing the viscosity of phosphate rock sus- U phosphoric acid compound.

pensions to low values suitable for drilling. 3. In the process of drilling wells, the step of We claim as our invention: introducing into a, well a drilling fluid comprising 1. A drilling fluid suitable for drilling wells 5 an aqueous suspension of crushed phosphate rock comprising crushed phosphate rock and an alkali and a. small percentage of a. water-soluble polypolyphosphate. phosphoric acid compound.

2. A drilling fluid for wells, comprising an TIREY FOSTER FORD.

aqueous suspension of crushed phosphate rock, ALBERT G. LOOMIS. 

